1. Field of the Invention
The present invention relates to a tire parameter estimation device and a road surface judgment device. More particularly, the present invention relates to a tire parameter estimation device and a road surface judgment device suitable for controlling the running of a vehicle.
2. Description of Related Art
It has been known to estimate tire parameters of tires of a vehicle and to control the running of the vehicle by using the tire parameters. The tire parameters include tire wear amount and tire temperature, for example.
Japanese Patent Application Laid-Open (JP-A) No. 5-332762, for example, discloses a tire abnormal wear detector to estimate the tire wear amount. This tire abnormal wear detector detects abnormal wear of the tire on the basis of the change in the number of revolutions of the tire when a dynamic radius of the tire becomes small due to the wear of the tire. More specifically, the correlation between a resonance frequency (dependent on air pressure) determined on the basis of output of a wheel speed sensor and the number of revolutions of the tire is obtained in advance while taking the change in the dynamic radius due to the air pressure of the time into account, the detector judges that the tire is worn out when the number of revolutions of the tire falling outside this correlation is detected.
However, there has been a problem that this tire abnormal wear detector is only able to detect the tire wear when the dynamic radius becomes uniformly small as the tire is uniformly worn out. Grip force of the tire drops due to the wear of a tire shoulder, for example, but this detector cannot detect such a wear.
Also, to estimate the tire temperature, Japanese National Publication No. 11-504585, for example, discloses a device in which a temperature sensor is provided with a tire housing to transmit a temperature measurement value obtained by this temperature sensor into, or outside, a vehicle compartment. However, this device requires exclusive components such as a slip ring and the temperature sensor to measure the tire temperature, which results in an increase in costs, and there have been problem with durability and reliability.
In addition, tire parameters, which are effected by external environment, such as road surface friction, are effected, by both characteristics of the vehicle and characteristics of the road environment. Moreover, because it is difficult to strictly distinguish between vehicular factors and environmental factors, it is very difficult to estimate the tire parameters by only the behavior of the vehicle and the road state.
It is generally difficult to judge road surface state unless the state of the tire is somehow made close to a critical region (maximum friction region). If such a control is made, however, a change in the behavior of the vehicle occurs, whereby vibration and noise arise, and driving ease and maneuverability deteriorate.
Road surface state can also be grasped by directly measuring the road by sensor disposed on the road, but sensors cannot be installed on an entire road from the aspect of cost. Sensors may be installed partially on the road, but there is no point in installing sensors partially because wear characteristics vary greatly depending on place of the road.
The present invention is devised in order to eliminate the problems described above. It is an object of the present invention to provide a tire parameter estimation device that is economical and can accurately estimate tire parameters while taking into consideration both vehicular states road and environment states. It is another object of the present invention to provide a road surface judgment device that can easily judge road surface states without having to expend cost on facilities for the road.
According to a first aspect of the present invention, there is provided a tire parameter estimation device, the device comprising: a wheel speed detecting section for detecting a wheel speed; a road surface friction parameter generating section for generating a road surface friction parameter representing a friction state between a tire of a wheel and a road surface on the basis of the wheel speed detected by the wheel speed detecting section; a memory section for storing the road surface friction parameter generated by the road surface friction parameter generating section; and a tire parameter estimation section for estimating at least one tire parameter relating to the tire and the road surface on the basis of the road surface friction parameter stored by the memory section and the road surface friction parameter newly generated by the road surface friction parameter generating section.
According to the first aspect of the invention, the road surface friction parameter generating section generates the road surface friction parameter on the basis of the wheel speed. Here, the road surface friction parameter and the road surface have the correlation, and the road surface friction parameter at the time when the vehicle is running on a reference road surface serves as a reference value. The tire parameter that represents the relation between the road surface and the tire depends on the change of the road surface friction parameter. The road surface friction parameter as the reference value is stored. The tire parameter can thus be estimated on the basis of this road surface friction parameter and the road surface friction parameter that is newly estimated.
According to a second aspect of the present invention, the tire parameter estimation device of the first aspect of the present invention further comprises a reference running state detecting section for detecting a reference running state of a vehicle, wherein the memory section stores the road surface friction parameter at a time at which the reference running state detecting section detects the reference running state, as a reference parameter, and the tire parameter estimating section estimates, as the tire parameter, a tire temperature corresponding to the road surface friction parameter newly generated by the road surface friction parameter generating section by using the characteristics of the tire temperature and the road surface friction parameter with respect to the reference parameter.
According to the second aspect of the present invention described above, the road surface friction parameter at the time when the vehicle is under the reference running state is stored as the reference parameter. When the tire temperature changes, the road friction parameter also changes. The tire parameter estimating section utilizes such a characteristics and estimates the tire temperature on the basis of the road surface friction parameter newly estimated during the vehicle running.
According to a third aspect of the present invention, the tire parameter estimation device of the first aspect of the present invention described above further comprises a reference running state detecting section for detecting a reference running state of a vehicle; a running start detecting section for detecting a start of running of the vehicle on the basis of the wheel speed detected by the wheel speed detecting section; and a writing section for writing into the memory section the road surface friction parameter generated by the road surface friction parameter generating section each time the running start detecting section detects the start of running of the vehicle and the reference running state detecting section detects the reference running state of the vehicle, wherein the tire parameter estimating section estimates a wear amount of the tire as the tire parameter on the basis of a change in a plurality of the road surface friction parameters stored in the memory section.
According to the third aspect of the present invention, the road surface friction parameter generated by the road surface friction parameter generating section is written into the memory section each time the running start judgment section detects the start of running of the vehicle and the reference running state detecting section detects the reference running state of the vehicle. Here, the tire wear amount changes in accordance that the road surface friction parameter changes. The tire parameter estimating section utilizes this characteristic and estimates the tire wear amount on the basis of the drop amount of the road surface friction parameter stored in the memory section.
According to a fourth aspect of the present invention, there is provided a road surface judgment device, the device comprising: a vehicle state detecting section for detecting a running state of a vehicle; a road surface friction state estimating section for estimating a road surface friction state of a road surface on which the vehicle is running, on the basis of the running state of the vehicle detected by the vehicle state detecting section; a road surface state measuring section for measuring a road surface state of the road surface on which the vehicle is running, on the basis of the running state of the vehicle detected by the vehicle state detecting section and a controlled state of the vehicle; a referencing section for corresponding the road surface friction state with the road surface state to obtain a reference value; a reference value changing section for changing the road surface friction state of the reference value to the road surface friction state estimated by the road surface friction state estimating section when the road surface state newly measured by the road surface state measuring section is the same as the road surface state of the reference value; and a road surface state judging section for judging the road surface state of the road surface on which the vehicle is currently running, on the basis of the road surface friction state newly estimated by the road surface state estimating section and the reference value processed through the reference value changing section.
According to the fourth aspect of the present invention, the road friction estimating section estimates the road surface friction state of the road surface on which the vehicle is running, on the basis of the running state of the vehicle detected by the vehicle state detecting section. The road surface state of the road surface on which the vehicle is running is measured, on the basis of the running state of the vehicle detected by the vehicle state detecting section and the control state of the vehicle. The road surface friction state and the road surface state thus obtained are associated with each other to give a reference value. Incidentally, when the vehicle again runs on the same road surface as the reference road surface, the road surface friction state of the reference value is changed to the road surface friction state estimated by the road surface friction state estimating section. In this way, the reference value is changed in such a manner as to correspond to the vehicle state and the road surface state. The road surface state judging section thus judges the road surface state of the road surface, on which the vehicle is currently running, on the basis of the road surface friction state newly estimated by the road surface state estimating section and the reference value processed through the reference value changing section.
According to a fifth aspect of the present invention, in the road surface judgment device of the fourth aspect of the present invention, the referencing section corresponds the road surface friction state at a time at which the vehicle is in a predetermined running state, with the road surface state.
According to a sixth aspect of the present invention, in the road surface judgment device of the fourth or fifth aspect of the present invention, the referencing section corresponds the road surface friction state, at a time at which the vehicle is running on a predetermined road surface, with the road surface state.
According to a seventh aspect of the present invention, there is provided a road surface judgment device, the device comprising: a vehicle state detecting section for detecting a vehicle running state; a receiving section for receiving road surface environment information relating to a reference road surface; a road surface state estimating section for estimating a road surface state of a road surface on which a vehicle is running, on the basis of the vehicle running state detected by the vehicle state detecting section; a memory section for storing, as a reference value with respect to the reference road surface, the road surface state estimated by the road surface state estimating section each time the receiving section receives the road surface environment information; and a judgment section for judging a state of a road surface other than the reference road surface, on the basis of the road surface state estimated by the road surface state estimating section and the reference value with respect to the reference road surface stored in the memory section, when the receiving section does not receive the road surface environment information.
According to the seventh aspect of the present invention, the road surface state estimating section estimates the road surface state of the road surface on which the vehicle is running, on the basis of the vehicle running state detected by the vehicle state detecting section. Each time the receiving section receives the road surface environment information, the memory section stores the road surface state estimated by the road surface state estimating section as the reference value with respect to the reference road surface. In other words, the memory section stores the road surface state at the time at which the vehicle is running on the reference road surface as the reference value. Consequently, the reference value for the reference road surface is updated to an optimal value in accordance with the change of the road environment. The road surface judgment device judges the state of road surface other than the reference road surface on the basis of the road surface state estimated by the road surface state estimating section and the reference value for the reference road surface stored in the memory section.
According to a eighth aspect of the present invention, in the road surface judgment device of the seventh aspect of the present invention, the memory section stores the road surface state estimated by the road surface state estimating section at a time at which the vehicle is in a predetermined running state, as the reference value with respect to the reference road surface.
According to a ninth aspect of the present invention, in the tire parameter estimation device of the second aspect of the present invention, the reference running state detecting section detects whether or not the reference running state of the vehicle, on the basis of: the road surface friction parameter; and whether or not the vehicle is in a predetermined state.
According to a tenth aspect of the present invention, in the tire parameter estimation device of the ninth aspect of the present invention, the predetermined state of the vehicle is at least one of that: the vehicle is running substantially straight; the vehicle is running in a substantially constant speed; a rotation vibration of the wheel is less than or equal to a predetermined level; a wiper of the vehicle is not operating; and a temperature outside the vehicle is more than or equal to a predetermined temperature.
According to an eleventh aspect of the present invention, in the tire parameter estimation device of the first aspect of the present invention, the device further comprises: a reference running state detecting section for detecting a reference running state of the vehicle; a running start detecting section for detecting a start of running of the vehicle on the basis of the wheel speed detected by the wheel speed detecting section; a time judging section for judging a time; and a writing section for writing into the memory section the road surface friction parameter generated by the road surface friction parameter generating section each time the running start detecting section detects the start of running of the vehicle, the reference running state detecting section detects the reference running state of the vehicle, and the time judging section judges a predetermined timing; wherein the tire parameter estimating section estimates a wear amount of the tire as the tire parameter on the basis of a change in a plurality of the road surface friction parameters stored in the memory section.
According to a twelfth aspect of the present invention, in the tire parameter estimation device of the first aspect of the present invention, the device further comprises: a reference running state detecting section for detecting a reference running state of the vehicle; a running start detecting section for detecting a start of running of the vehicle on the basis of the wheel speed detected by the wheel speed detecting section; and a writing section which can write into the memory section the road surface friction parameter generated by the road surface friction parameter generating section when the running start detecting section detects the start of running of the vehicle and the reference running state detecting section detects the reference running state of the vehicle; wherein the tire parameter estimating section estimates a wear amount of the tire as the tire parameter on the basis of a change in a plurality of the road surface friction parameters stored in the memory section.
According to a thirteenth aspect of the present invention, in the road surface judgment device of the fourth aspect of the present invention, the device further comprises a memory section for storing the reference value and the reference value changed by the reference value changing section.
According to a fourteenth aspect of the present invention, the road surface judgment device comprises: a vehicle state detecting section for detecting a running state of a vehicle; a road surface friction state estimating section for estimating a road surface friction state of a road surface on which the vehicle is running, on the basis of the running state of the vehicle detected by the vehicle state detecting section; a road surface state measuring section for measuring a road surface state of the road surface on which the vehicle is running, on the basis of the running state of the vehicle detected by the vehicle state detecting section; a referencing section for corresponding the road surface friction state with the road surface state to obtain a reference value; a reference value changing section for changing the road surface friction state of the reference value to the road surface friction state estimated by the road surface friction state estimating section when the road surface state newly measured by the road surface state measuring section is the same as the road surface state of the reference value; and a road surface state judging section for judging the road surface state of the road surface on which the vehicle is currently running, on the basis of the road surface friction state newly estimated by the road surface friction state estimating section and the reference value processed through the reference value changing section.